The urban and suburban trees of Chicagoland face an array of insect challenges — some native, some invasive, some newly arrived. Effective pest management starts with correct identification, because different insects require fundamentally different approaches, and applying the wrong treatment wastes money and can cause additional harm.
Emerald Ash Borer (Agrilus planipennis)
The most destructive invasive tree insect in Illinois. EAB larvae feed beneath the bark of ash trees, disrupting water and nutrient transport. Without treatment, most ash trees die within 3 to 5 years of infestation. Treatment options include trunk injections of emamectin benzoate (2-3 year residual) or systemic soil applications of imidacloprid. Early treatment is critical — trees with more than 50% canopy decline have limited treatment success.
Japanese Beetle (Popillia japonica)
Adult beetles feed on foliage and flowers in July and August, creating a characteristic "window paning" pattern as they eat the tissue between leaf veins. Heavy infestations can defoliate trees. Systemic insecticides applied as soil treatments in late spring or early summer are the most effective control for trees.
Bronze Birch Borer (Agrilus anxius)
A close relative of EAB, the Bronze Birch Borer targets stressed birch trees. Larvae bore under the bark in the upper crown first, causing progressive dieback from the top down. Birch trees stressed by drought, poor soil, or improper planting are most vulnerable. Treatment with systemic insecticides works for trees with less than 30% dieback, but preventing stress through proper care is the best defense.
Scale Insects
Scales are small, often immobile insects that attach to stems and feed on plant sap. There are two types: armored scales (like oystershell scale) which have a hard protective covering and don't produce honeydew, and soft scales (like cottony maple scale) which excrete honeydew that leads to sooty mold on leaves and surfaces below. Treatment timing is critical — scales are most vulnerable during the "crawler" stage when young scales are mobile and have not yet formed their protective covering.
Sooty mold is not a disease that attacks your tree directly — it grows on honeydew produced by sucking insects like scales, aphids, or leafhoppers. If you see black sooty deposits on leaves, look for the insect pest that's causing the honeydew production.
Spider Mites
Spider mites are technically arachnids, not insects, but they are significant tree pests. They thrive in hot, dry conditions and cause stippled, bronzed foliage. Spruce spider mites prefer conifers and are most active in cool weather; two-spotted spider mites are more common on deciduous trees in summer. Miticides are specific treatments; most general insecticides do not control mites and may actually make infestations worse by killing predatory insects.
Aphids
Aphids feed on new growth and phloem sap, often in large colonies. They produce copious honeydew and can cause leaf curling and distortion. However, aphids also have significant natural predator populations — lady beetles, lacewings, and parasitic wasps. In many cases, patience is the correct response; the predator population will catch up to the aphid population within a few weeks. Unnecessary insecticide applications kill predators and can make aphid problems worse the following year.
Integrated Pest Management
Good pest management uses an integrated approach: proper identification, understanding pest biology and life cycles, cultural controls (proper planting and care to reduce tree stress), biological controls (supporting natural predator populations), and chemical controls only when necessary and at the right time. A certified arborist with plant health care training develops treatment programs tailored to the specific pest, tree species, and situation.
If you're seeing unusual symptoms on your trees — unexplained dieback, discolored foliage, or canopy thinning — contact Emerald Tree Care for a diagnosis. Our plant health care specialists serve Western Chicagoland and can identify the problem and develop an effective management plan.
